1. Field of the Invention
The present invention relates to a method for producing a thin film transistor, and particularly relates to a method, rather than a semiconductor process, for producing a thin film transistor.
2. Background of the Invention
A conventional method for producing a conventional thin film transistor uses semiconductor technology, which includes film deposition, photolithography technology, etching processes and the like. The film deposition process includes deposing a film of dielectric or insulating material by chemical vapor deposition (CVD) and deposing a film of electric material by physical vapor deposition (PVD). The photolithography and the etching processes define a pattern thereof. The equipment used for film deposition, photolithography and etching processes are all high-priced. As such, semiconductor technology, which consumes a lot of time and labor and requires expensive paraphernalia, is often criticized.
Referring to FIGS. 1A to 1D, the first prior art, a conventional photosensitive pressing method, illustrates a transparent plate 1a having a protrusion projected therefrom. The protrusion is transparent. A photosensitive material 3a is then poured between the transparent plate 1a and a glass substrate 2a. The transparent plate 1a and a glass substrate 2a are separated yet are close to each other. Next an ultraviolet light is provided to cure the photosensitive material 3a, which has been shaped between the transparent plate 1a and the glass substrate 2a. After a dry or wet etching process, a resident part of the photosensitive material 3a will be removed, to form a pattern of a thin film transistor. However, by this stage all parts of the photosensitive material 3a have been cured because of the transparent protrusion, so the etching process is necessary. Furthermore, the transparent protrusion still plays another role as a photoresist that controls the depth of the pattern of the thin film transistor.
FIG. 2, a perspective view of a second prior art, U.S. Pat. No. 6,518,189, discloses a first conventional nanoimprint method. An opaque plate 1b has a protrusion projected therefrom, and presses onto a layer of thermoplastic polymer materials 3b that is coated on a substrate 2b in advance. Thermoplastic polymer materials 3b, only melt at high temperatures (more than 300 degrees centigrade) and shaping requires large amounts of pressure. As such any press equipment that is used in the process should be resistant against the testing environment of these kinds of conditions. In addition, the layer of thermoplastic polymer materials 3b is cured after a cooling process and is further shaped by an etching process to produce a pattern.
With respect to FIG. 3, a perspective view of the third prior art, U.S. Pat. No. 5,900,160, discloses a first conventional microcontact method. A turbine mold 1c presses onto a substrate 2c that has a layer of micro-materials 3c in a rotating manner. This method however, lacks a precise and stable alignment. Furthermore, the mold 1c is made of Polydimethylsiloxane (PDMS) that wears out easily, deforms and has a negative effect on the precision of the pattern thereof.
The fourth prior art is displayed in FIGS. 4A to 4D which illustrate sequential perspective views as disclosed in U.S. Pat. No. 6,060,121, as a second conventional microcontact method. A plate 1d having a protrusion projected therefrom and an impression coating 3d formed thereon, presses a substrate 2d coated with a thin film 4d. Although a pattern is formed, the thickness of the pattern is much thinner that that of other conventional methods necessitating an additional process with another material in order to increase the thickness of the pattern.
The fifth prior art is displayed in FIGS. 5A to 5D which illustrate sequential perspective views as disclosed in U.S. Pat. No. 6,380,101, as a third conventional microcontact method. A plate 1e having a protrusion projected therefrom and an impression coating 3e formed thereon, presses a substrate 2e coated with a thin film 4e. Similarly to the first prior art, the impression coating 3e is further provided as a photoresist for post etching process.
The sixth prior art is displayed in FIGS. 6A to 6D which illustrate sequential perspective views as disclosed in U.S. Pat. No. 6,413,587, as a fourth conventional microcontact method. A plate if having a protrusion projected therefrom and an impression coating 3f formed thereon, presses a substrate 2f coated with a thin film 4f. Similarly to the fourth prior art, an additional process is necessary with another material in order to increase the thickness of the pattern because of the thin impression coating 3f. 
In regards to the conventional microcontact methods according to the third to the sixth prior arts, the first step is to produce an impression mold made of polymer materials as the plate or mold for providing sufficient deformation in the pressing step. The impression mold should separate easily from the substrate after the pressing step. The impression mold however, often suffers from defective patterns due to the resilient property caused by the pressure that it experiences in the pressing step. So the pattern is often imprecise. Additionally, the impression mold reacts easily with non-polar organic solvents, such as toluene or hexane. When this occurs, the impression mold expands by a volume thereof due to its chemical property. As such, the peripheral environment should be controlled and monitored.
Hence, an improvement over the prior art is required to overcome the disadvantages thereof.